Treatment of carbonaceous solids



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snvenbor 2255 Qbborncg Patented Sept. 16, 1952 UNITED STATES ATENT OFFICE TREATMENT OF CARBONACEOUS SOLIDS Charles E. Hemminger, Westfield, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Claims.

The present invention relates to the treatment of carbonaceous solids or semi-solids to produce volatile combustibles. More particularly, the invention is concerned with the carbonization of such carbonizable materials of low ash content and high volatility as bituminous coal, lignite, asphalts and pitches in a finely divided form to produce coke and valuable volatile products such as combustible gases and liquids.

This application is a continuation-in-part of my copending application Serial No. 702,991, filed October 12, 1946.

Heretofore, carbonaceous materials of the type specified above have been converted into liquid and gaseous fuelsand cake by fixed bed coking processes. These processes either require frequent cleaning periods resulting in discontinuous operation or they involve ineflicient conversion of the available carbon into heat and. volatile fuels.

The operation of these processes may be made fully continuous by employing the fluid solids technique in which the reaction takes place in a dense fluidized bed of finely divided solids maintained in a turbulent ebullient state by means 01 fiuidizing gases. This technique has highly desirable additional advantages including greatly improved heat distribution and ease of solids handling. Heat may be supplied by a combustion of portions of the carbonaceous charge either within the reactor or in a separate fluid heater from which hot solid combustion residue is returned to the reactor.

While this procedure affords a greatly improved utilization of available carbon, considerable losses of process materials are incurred in the form of carbonaceous fines entrained in the product vapors withdrawn from the reactor and inseparable by conventional gas-solids separation means. This not only causes an appreciable reduction in process yields but, in addition, complicates the handling of the tar.

Furthermore, it has been found that fines en trainment from fluidized solids beds consisting of coal, and coke particles within the fluidizable range is so excessive as to interfere seriously with the operability of this type of process. More specifically, experiments have demonstrated that the entrainment rat from a char bed consisting of particles ranging in size from about 5-1000 microns, with about 80% larger than 80 microns and fluidized at superficial linear gas velocities or about 0.2-2 ft. per second may run as high as 1.0 lb. of solids per cu. ft. of gasiform overhead. Similar conditions prevail in fluid coal carbonization because the fluidized solids in the carbonizer consist predominantly of char during normal 2 operation. Entrainment rates of this magnitude interfere with proper fluidization and cause prohibitive solids'losses. i

In. commercial coke oven practice, the volatile carbonization products containing suspended carbonaceous solids fines are introduced into a water seal for cooling and simultaneous scrubbing of solids fines from the resulting gas. I-Iowever, this procedure is highly inefiicient with respect to solids recovery and heat economy and, therefore, unsuitable for fluid operation involving substantially higher entrainment ratesthan commercial coke oven practice which employs fixed bed operation. I 1

The present invention overcomes the aforementioned difiiculties and affords variousadd'itional advantages. These advantages, the nature of'th'e' invention and the manner in which it is carried out will be fully understood from the following description thereof read with reference to. the accompanying drawing.

It is an important object of the present invention to provide an improved process for carbonizing carbonizable solids of the type specifled employing the fluid solids technique.

Another object of the invention is to provide an improvedcarbonization process employing the fluid solids technique wherein no losses in the form of solids entrained in product vapors are incurred.

Other objects and advantages of the invention will appear hereinafter.

In accordance with the present invention, the productvapors and gases resulting from a fluid" carbonization zone operated at tar cracking conditions and carrying entrained carbonaceous solids are subjected in a scrubbing zone to the scrubbing action of liquid product tar bottoms which remove entrained solids from the gases. The scrubbing treatment is preferably carried out at a temperature substantially above the boiling point of the highest boiling carbonization products desired for recovery, that is above about 500 F., and the preferred scrubbing liquid comprises at least substantial amounts of tar boiling above said temperature and preferably above 700 F. At leasta portion of the scrubbing tar containing the solids fines is returned to the carbonization zone. In thismanner, losses of carbonaceous solids are substantially reduced or completely avoided and undesirable heavy tar fractions are further converted by cracking into more valuable gases, light oils and coke.

In. addition, the fines entrainment from the fluidized bed in the carbonization zone is substantially reduced when operating in accordance with the invention. The solids entrained at standard fiuidization conditions consist predominantly of particles of 40 microns and mostly of particles of 20 microns. When these entrained fines are scrubbed from the overhead suspension byproduct tar they are wetted and im pregnated with tar. Upon recycling to the carbonization stage the fines so impregnated a glomerate and are baked together to form aggregates of a particle size much larger, usually about 2-5 times larger, than that of entrained particles. The result is that the scrubbed fines are converted into particles of mostly 40+ microns size whereby the ratio of intermediate and coarse particles to fines in the carbonizer is substantially increased and fines entrainment is correspondingly reduced.

Various external oils may be added to the scrubbing zone to decrease the viscosity of the scrubbing tar and increase its fluidity in the presence of the carbonaceous solids fines. External oils suitable for this purpose include refractory gas oils such as heavy catalytic cycle gas oils, residual fuel oils or other liquid bitumina which are useful only as fuels and, therefore, hi hly economical in the present process because they may be converted into valuable fuel gases and light oils when recycled to the carbonization zone.

The temperature of the scrubbing zone may be readily adjusted within the limits of, say, about 500 and 800 F. so as to adiust the recovery of light oils and tars as overhead from the scrubbing zone and the character of the scrubbing tar to any desired ratio in accordance with fluctuating market demands and the requirements of the process.

As stated above, an advantage of the process of the invention resides in the fact that all or the major part of the heavy tar bottoms may be recycled to the carbonization zone and converted into additional amounts of light oils and gases. On the other hand, when lar er yields of heavy tar are desired the bottoms of the scrubbing zone may he sett ed in conventional settlers such as Dorr thickeners and only a material highly concentrated in carbonaceous solids fines recycled to the carbonization zone while excess scrubbing tar becomes availab e far marketing.

Having set forth its general nature and objects, the invention will be best understood from the subseouent more detailed description in which reference will be made to the accompanyin drawing which shows a semi-dia rammatic illustration of a aratus adapted to carry out a preferred embodiment of the invention.

Referrin now to the drawing. the system shown therein essent ally-comprises a fluid coker in, a product scrubber 30, a gas scrubber 10 and a still 80, the functions and cooperation of which will be presently described.

In operation. finely divi ed carbonization coal, such as a hi hly volati e bituminous coal. is fed by means of a conventional feed hopper. screw conveyor or aerated standpipe (not shown) to line I and from there to coker ID. The particle size of the coal may vary from less than 100 mesh up to A1 or /2 in. diameter.

Coker In which is essentially of cylindrical shape is preferably provided with a conical bottom l2 separated from the cylindrical main section by a grid or other foraminous member I4. The coal supplied by line I forms above grid [4 a dense, turbulent, ebullient mass of solids fluidized by a gas admitted through line l8 to form a well defined upper level [6.

The gas admitted through line 18 may be superheated steam having a temperature sufficiently high to heat the fluidized coal in coker I to the desired carbonization and cracking temperature of, say, about 800-1600". F. If desired, an oxidizing gas such as air and/or oxygen may be supplied through line l8 in place of, or in addition to, the steam to generate heat within coker I0 by a partial combustion of combustible coal constituents. All or part of the heat required may also be supplied by internal heating coils carrying a heating medium as described and claimed in the copending application, Serial No. 690,818 filed August 15, 1946. However, no matter in what manner that heat required is supplied to coker I0, sufllcient gas such as steam, flue gas, or the like must be supplied through line l8 to maintain the solids bed in coker 10 in a fluidized state. For this'purpose the gas in coker I0 should have a superficial velocity falling within the approximate limits of 0.1 and ft. per second to obtain a fluidized mass having a density of about -50 lbs. per cu. ft.

The pressure in coker [0 may be readily so chosen that the cracking conversion of heavy carbonization products into gases, light oils and coke is favored. Such pressures may fall within the approximate limits of 5-100 lbs. per sq. in. gauge at the temperatures here specified.

Finely divided coke is withdrawn downwardly from coker I0 through pipe 20 and may be passed to a water gas producer, a briquetting plant or other conventional coke utilization means (not shown). I

Volatile carbonization products and entrained carbonaceous solids fines pass overhead from level 16 through a conventional gas-solids system 22 from which separated solids may be returned through pipe 24 to coker [0.

The product vapors and gases leaving separator 10 still contain substantial amounts of carbonaceous fines entrained therein. This suspension of solids fines in vapors and gases is passed through line 28 to the lower portion of scrubber 30,

The flow conditions and design of scrubber 30 are so chosen that scrubbed volatile products leave overhead at a temperature of, say, '500-800f F. at which the heaviest portions of the tar condense so as to act as the scrubbing agent for the volatile products and to remove the solids fines therefrom.

Rich scrubbing tar is drawn oflf the bottom of scrubber 30 through line 32. A portion ofthe withdrawn tar is passed through line 34 and cooler 36 and returned through line 38 by means of pump 40 to the upper portion of scrubber 30 to serve as reflux condensate and to establish the desired temperature in scrubber 30. Reflux ratios of about 1 to 10:1 are suitable for this purpose at temperatures of 200 to 600 F. in cooler 36. If desired, the viscosity of the condensate of scrub ber 30 may be reduced by adding a diluting oil such as an oil of the gas oil boiling range through line 44.

At least a substantial portion of the remainder of the tar containing scrubbed solids withdrawn through line 32, usually amounting to about 25-100%, is recycled through line 46 by means of pump 48 to coker I0. In this manner, the whole or a part of the carbonaceous solids fines en- I trained in the volatile carbonization products are is passed on by pump 58 at about/theasame pres.-

sure, recombined with the compressed gases in line 60 and-fed to a second knock-out drum 62 from which intermediate tar fractions are with drawn as bottoms through line 64. Overhead from drum .62 passes through, line 65 to a gas scrubber 19 wherein the-gases arefurther cooled to about.5.0- l50 F bymeansofa properly cooled reflux arrangement in a manner known per se. The gases taken overhead from scrubber through line- 12 are ready for any desired use, such as city gas, feed gas for synthesis processes, further treatment to produce mixtures ofGQa-nd H'z-e. g; by reformation, etc.

The bottoms from scrubber '10 pass through line 14 to a still 80 wherein they may be fractionated or steam distilled in any desired conventional manner and in accordance with market demands.

While referring above mainly to bituminous starting materials which are solid at the carbonization conditions, the invention is not limited to such materials. Carbonizable materials which are liquid at the carbonization conditions maybe sprayed and coked on finely divided inert solids, particularly coke, maintained as a fluidized bed in coker Hi. The remaining procedure is substantially that described above as will be understood by those skilled in the art.

The invention will be further illustrated by the following specific examples.

EXAMPLE I A fluid coker of the type described above is operated in a continuous manner at a temperature of about 1000 F., a pressure of about 10 lbs. per sq. in. and a fluid bed density of about lbs. per cu. ft. using Pittsburgh seam coal having an average particle size of about 100 mesh. The voaltile coker overhead, after passage through a conventional cyclone separator, contains about 2% by weight of the coal charged in the form of coke fines after equilibrium conditions have been reached. This overhead is charged to a scrubber of the type described above which is operated as follows:

Scrubber operation Pressure 10 lbs. per sq. in. gauge.

Scrubber top tempera- 510 F.

ture.

Coke recycle to coker 2% by weight of coal charged.

Tar (B, P. 700 F.+) re- 15% by weight of coal cycled to coker. charged.

:Flar (B P. 700 F.+) re- 30% by weight of coal cycled to scrubber. charged.

Temperature of scrub- 200-250 F.

ber recycle.

6:. Atthese:conditionsizthe productyields-aresabout asiollows: J m, 1

Product 65 Charged;

Gas;- 19.3.0 LightQi1 0.55 Tar'tRecovcrod' at 64) 5:10 ammonia-lemming-.. nlwmnmnnmw 5:80 Coke M I 79.115

I The. compositionoi the-tar isapproximatelyas fol-lows: 4

Pitch (over TWP.) '0 volume percent;

Benzene-insoluble residue 0 .per-centby weight;

The gas. which amounts .to.about.-5,0,00 .cuit. pertonoi coal. has a. heating value of about .800 Br 1;. ugper cu. ft. and a specific gravity of about 0.5 Air,==l). v

1 EXAMPLEII.

Operation without tar and solids recycle-ztoczthe coker at otherwise identical conditions produces approximately the following yields:

The tar cut boiling between and 700 F. amounts to 44% of the total tar and has about the following composition:

Volume per cent Bases 2 Acids 27 Aromatics 37 Parafiins+naphthenes 34 The pitch (over 700 F.) amounts to 56% of the tar and contains a benzene-insoluble residue of 22% by weight. I

The gas, which amounts to about 4600 cu. ft. per ton of coal charged, has a heating value of about 800 B. t. u. per cu; ft. and a specific gravity of about 0.53 (A.ir=1).

It will be noted that the lower tar yield of Example I is more than compensated by its higher quality as well as by the higher coke, gas and light oil yields, as compared with Example II.

The foregoing description and exemplary operations have served to illustrate specific appli- 800'-1600' F. and elevated pressures IOf about -100 p. s. i. g. conducive to the cracking conversion of carbonization products of undesirably high boiling point into gases, light oils and coke, withdrawing volatile carbonizationiproducts containing entrained carbonaceous solids fines upwardly from said zone, scrubbing said volatile products in a scrubbing zone at a temperature above the boiling point of the highest boilingvolatile carbonization products desired for recovery with a hydrocarbonaceous liquid comprising substantial proportions oi'condens'ed carboniz'ation products boiling above about 700 F. to remove entrained solids fines from said volatile products, recovering volatile products free of entrained-solidsfrom' saidscrubbing zone, and recycling used scrubbing liquid containing said entrained solids in suspension to said carbonization zonewhereby said scrubbed fines are impregnated by said scrubbing liquidand agglomerated in the course of said recycle procedure to form particles of substantially greater size than that of said entrained fines, recycled scrubbing liquid being cracked to form lighter products in said carbonization zone.

2. The process of claim 1 in which said liquid also contains an external hydrocarbon oil of lower viscosity than said condensed carbonization products.

8 3.'The process of claim 1 wherein used scrubbingliquid is withdrawn from said scrubbing zone,. cooled to a temperature suitable for said scrubbing action and returned to said scrubbing zone. a

4. The process of claim 1 in which said material is bituminous coal of fluidizable particle size and said carbonaceous solids comprise coke formed in said zone from said coal.

. 5'. The process of claim 1 in which said material is liquid at said carbonization temperature and said carbonaceous solids consist essentially of coke, said material being sprayed in the liquid state onto said fluidized bed.

CHARLES E. HEMMINGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,908,133 Eglofi May 9, 1933 2,388,055 Hemminger Oct. 30, 1945 2,396,036 Blanding Mar. 5, 1946 2,406,810 Day Sept. 3, 1946 

1. THE METHOD OF CARBONIZING A BITUMINUOUS MATERIAL OF HIGH VOLATILITY AND LOW ASH CONTENT WHICH COMPRISES FEEDING SAID MATERIAL IN SUBDIVIDED FORM TO A DENSE TURBULENT FLUIDIZED BED OF CARBONACEOUS SOLIDS MAINTAINED IN A CARBONIZATION ZONE, PASSING A GAS UPWARDLY THROUGH SAID BED AT CARBONIZATION TEMPERATURES OF ABOUT 800*-1600* F. AND ELEVATED PRESSURES OF ABOUT 5-100 P. S. I. G. CONDUCTIVE TO THE CRACKING CONVERSION OF CARBONIZATION PRODUCTS OF UNIDESIRABLY HIGH BOILING POINT INTO GASES, LIGHT OILS AND COKE, WITHDRAWING VOLATILE CARBONZATION PRODUCTS CONTAINING ENTRAINED CARBONACEOUS SOLIDS FINES UPWARDLY FROM SAID ZONE, SCRUBBING SAID VOLATILE PRODUCTS IN A SCRUBBING ZONE AT A TEMPERATURE ABOVE THE BOILING POINT OF THE HIGHEST BOILING VOLATILE CARBONIZATION PRODUCTS DESIRED FOR RECOVERY WITH A HYDROCARBONACEOUS LIQUID COMPRISING SUBSTANTIAL PROPORTIONS OF CONDENSED CARBONIZATION PRODUCTS BOILING ABOVE ABOUT 700* F. TO REMOVE ENTRAINED SOLIDS FINES FROM SAID VOLATILE PRODUCTS, RECOVERING VOLATILE PRODU CTS FREE OF ENTRAINED SOLIDS FROM SAID SCRUBBING ZONE, AND RECYCLING USED SCRUBBING LIQUID CONTAINING SAID ENTRAINED SOLIDS IN SUSPENSION TO SAID CARBONIZATION ZONE WHEREBY SAID SCRUBBED FINES ARE IMPREGNATED BY SAID SCRUBBING LIQUID AND AGGLOMERATED IN THE COURSE OF SAID RECYCLE PROCEDURE TO FORM PARTICLES OF SUBSTANTIALLY GREATER SIZE THAN THAT OF SAID ENTRAINED FINES RECYCLED SCRUBBING LIQUID BEING CRACKED TO FORM LIGHTER PRODUCTS IN SAID CARBONIZATION ZONE. 